Problem: $ { \left[\begin{array}{rr}{0} & {-1} \\ {2} & {0} \\ {2} & {-1}\end{array}\right]+\left[\begin{array}{rr}{-2} & {2} \\ {-1} & {-2} \\ {2} & {1}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{0}+{-2} & {-1}+{2} \\ {2}+{-1} & {0}+{-2} \\ {2}+{2} & {-1}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-2} & {1} \\ {1} & {-2} \\ {4} & {0}\end{array}\right]}$